1. Field of the Invention
The invention is a connecting rod and piston assembly for use in internal and external combustion engines and in reciprocating compressors. It comprises the reciprocating linkage rotatively connected to the crankpin of a crankshaft which may have a plurality of such crankpins and connecting linkage. In the design presented the piston speed on the initial downstroke varies from the terminal speed on the upstroke as measured at corresponding angular stations symmetrical on each side of the top-dead-center position of crank rotation. For this reason the invention may also be classified as a variable-stroke engine.
2. Description of Prior Art
The reciprocating components of most piston driven engines are mechanically described as four-bar linkages with a sliding member and essentially comprising the elements of a crank, a connecting rod and a piston. There are however, other types of reciprocating linkages which are more complex. One example is an engine which employs a crosshead mechanism which is mounted below the piston and moves simultaneously in a transalatory path parallel with the piston. The purpose of the crosshead in previous designs has in general been to facilitate the sealing of the crankside of the cylinder in compound engine systems.
The present invention also employs a crosshead mechanism, but in this application its purpose and general operation are much different than the earlier use described. In the design presented the crosshead, hereinafter termed the "piston-slide", is slidably mounted in the piston crown. Its purpose is to provide a pivot-point for the connecting-rod in a manner which is independent of the piston wrist pin, hereinafter termed the "piston-pin", and to also compensate for cyclic changes in the connecting rod effective length as measured from the axial center of the piston-pin to the axial center of the crankpin.
Previous investigators, Mallory, U.S. Pat. No. 1,379,115 and McWhorter U.S. Pat. Nos. 3,859,976 and 3,908,623 also used piston slides for this purpose in the design of variable stroke engines. In these designs the piston slides were slidably mounted in the piston skirt or in the piston crown in a manner similar to the present invention and were also used to compensate for cyclic changes in the effective length of the connecting rod resulting from the class 1 and class 2 lever action linkage which was pivotally attached to the piston pin.
In the present invention the piston pin is pivotally mounted in a carrier which slides laterally to the right or to the left within an inclined slot provided at the upper end of the connecting rod. The pivotal action of the connecting rod at the piston end, resulting from changes in angularity with rotation of the crank, is performed by a second pin, hereinafter termed the "pivot pin". The pivot pin is pivotally mounted in the piston slide which is in turn slidably mounted in a machined surface within the piston crown. The primary difference between the present invention and those previously referenced is the use of a carrier working within an inclined slot which is used as a means of raising and lowering the piston pin instead of pivotal linkage. This type of design reduces the weight of the reciprocating mass by eleminating the use of heavier pivotal linkage and therefore reduces the dynamic loads, particularly at high engine speed.
The sliding movement of the carrier within the inclined slot of the connecting rod causes the distance between the axial centers of the piston pin and crankpin to vary in a manner which is proportional to the degree of inclination of the slot relative to the angular position of the connecting rod. Because the piston follows the motion of the piston pin an additional degree of control of piston motion is therefore achieved by the invention. Although the amount of augmenting piston motion achieved by the additional linkage is slight, it is very advantageous--particularly when the piston is near the top-dead-center position of the crank rotation where the clearance volume above the piston crown is small. At this position, very slight changes in piston motion will most significantly effect temperature and pressure within the small volume of the clearance and can therefore be used to beneficially influence the conditions of ignition and the post-ignition conditions of the combustion reaction.
The invention can be used to slow the piston speed during the initial downstroke of the combustion period. Combustion is therefore achieved at conditions which more closely simulate the efficiency of the theoretical constant volume process. Operation in this manner increases the mean effective operating pressure of the engine and thereby increases the overall thermal efficiency of the working process.
The invention can also be used to slow piston motion at the bottom-dead-center position of crank rotation. This provides additional piston dwell during the initial exhaust blowdown and during the terminal induction period thereby decreasing the amount of pumping work required during the exhaust cycle and increasing the volumetric efficiency of the induction cycle. The additional piston dwell at bottom-dead-center increases the efficiency of the mass transfer processes of the 2-stroke engine cycle and is also effective in increasing the volumetric efficiency of reciprocating compressors.